This invention relates to the preparation of keto steroids from .alpha.,.beta.-unsaturated keto steroids.
.alpha.,.beta.-Unsaturated keto steroids within the scope of this invention are understood to mean those steroids having at least one double bond in conjugation to a keto group, such as, for example, .DELTA..sup.4 -3-keto, .DELTA..sup.1 -3-keto, .DELTA..sup.1,4 -3-keto, .DELTA..sup.8 -11-keto, steroids.
The term "steroid" is to be used in its broadest sense, e.g. derivatives based on the cyclic ring system known as perhydro-1,2-cyclopentanophenanthrene. It includes, for example, those steroids mentioned in "Steroids", Fieser and Fieser, Reinhold, New York, 1959. In view of the continuing research in this area, it would not be possible nor would it be necessary for the purposes of this invention, to catalog all the different types of steroids that are known.
A conventional reaction for the reduction of .alpha.,.beta.-unsaturated ketones is the metal ammonia reduction, "Steroid Reactions, An Outline for Organic Chemists", Djerrassi, Holden-Day Inc., San Francisco, 1963, pages 299-315. This reaction is less than totally satisfactory for several reasons -- one reason being that it is necessary to handle potentially dangerous elemental alkali metal, and another reason being the production of a mixture of stereoisomers instead of one product.
It is also known that the electrochemical reduction of .alpha.,.beta.-unsaturated keto steroids in aqueous alcohol leads to the corresponding pinacols not to the corresponding saturated keto steroids (A. Kabasakalian et al, J. Amer. Chem. Soc. 78, 5032 [1956]; H. Lund, Acta Chem. Scand. 11, 283 [1957]; p. Bladon et al, J. Chem. Soc. 1958, 863; P. Bladon et al, ibid. 1962, 2352; P. Kabasakalian et al, J. Elektrochem Soc. 105, 261 [1958]; P. Zumann, ibid. 105, 758 [1956]).